How to start a timer after an update

 I have this timer script that works fine and is displayed on text but the timer starts as soon as I hit the play button instead of when my LaunchLane1 Function is triggered.In case you're wondering the LaunchLane1 function in being called from another script and it does work. I have tried to put the whole timer code inside a boolean called IsLaunched but still the timer runs even when not launched.
 import UnityEngine.UI;
 
   var crossedTheLine: boolean;
 public var startTime : float;
 public  var textTime : String;
 public  var TimeText : Text;
  var IsLaunched : boolean;
   
   
   
 function Start (){
 
 IsLaunched = false;
 }
 
  crossedTheLine = false;
  
  function Update (){
    //tried this but it doesnt work
   // if (IsLaunched == false){
 //   TimeText.text = "0";
   }
  
  
  
   function OnGUI (){
   if (!crossedTheLine)
  {
   
   
   
   
      var guiTime = Time.time - startTime;
   
      var minutes : int = guiTime / 60;
      var seconds : int = guiTime % 60;
      var fraction : int = (guiTime * 100) % 100;
  
       textTime = String.Format ("{0:00}:{1:00}:{2:00}", minutes, seconds, fraction);
   
        TimeText = GetComponent.<Text>();
        
       TimeText.text = textTime;
     
  }
   }
   function LaunchLane1 () {
    startTime = 0;
     textTime = "0";
   IsLaunched = true;
   }